The present invention relates to a linear compressor driving apparatus and, more particularly, to an apparatus for driving a linear compressor which generates a compressed gas in a cylinder by making a piston reciprocate with a linear motor.
A linear compressor utilizing a mechanical elastic member or elasticity of a gas has conventionally been known as an apparatus for generating a compressed gas.
FIG. 7 is a cross-sectional view for explaining a conventional linear compressor, and illustrates a concrete configuration of a linear compressor using a spring as an elastic member.
A linear compressor 100 has a cabinet 71 comprising a cylinder section 71a and a motor section 71b which are adjacent to each other. The cylinder section 71a of the cabinet 71 forms a cylindrical-shaped cylinder of the linear compressor 100. In the cylinder section 71a, a piston 72 is provided slidably along a direction parallel to a center axis of the cylinder (the piston axis direction).
On the back of the piston 72 in the cabinet 71, a piston rod 72a is placed in the cylinder section 71a and the motor section 71b, and an end of the piston rod 72a is fixed to the piston 72. Further, a support spring (resonance spring) 81 is placed between the other end of the piston rod 72a and an inner wall 71b1 of the motor section 71b which is opposed to the piston rod 72a. The support spring 81 deforms when the piston 72 is displaced from a piston neutral position (piston reference position), and, when the support spring 81 is deformed, the support spring 81 applies a force to the piston 72 so that the piston 72 returns to the piston reference position. Further, the piston neutral position is a piston position where the support spring 81 is not deformed, and no force is applied from the support spring 81 to the piston 72 when the piston 72 is located in the piston neutral position.
Further, a magnet 73 is fixed to a portion of the piston rod 72a, which portion is located in the motor section 71b, and an electromagnet 74 comprising an outer yoke 74a and a stator coil 74b, embedded in the outer yoke 74a is fixed to a portion of the inner wall of the motor section 71b, which portion is opposed to the magnet 73.
A linear motor 82 is constituted by the electromagnet 74 and the magnet 73. That is, in the linear compressor 100, the piston 72 reciprocates along its axis direction by the driving force of the linear motor 82, i.e., the electromagnetic force generated between the electromagnet 74 and the magnet 73, and the elasticity of the support spring 81.
On the other hand, a compression chamber 76, which is a closed space surrounded by a cylinder upper portion inner wall 75, a piston compression wall 72b, and a cylinder peripheral wall 77, is formed at the cylinder head side of the cabinet 71. An end of a cooling medium inlet tube 1a for drawing a low-pressure cooling medium gas into the compression chamber 76 is opened at the cylinder upper portion inner wall 75 and, further, an end of a tooling medium discharge tube 1b for discharging a high-pressure cooling medium gas from the compression chamber 76 is opened at the cylinder upper portion inner wall 75. An inlet valve 79 and a discharge valve 80 for preventing a back flow of the cooling medium gas are fixed to the cooling medium inlet tube la and the cooling medium discharge tube 1b, respectively.
In the linear compressor 100 having the above-described structure, the piston 72 reciprocates in its axis direction by an intermittent supply of a driving current from a motor driver (not shown) to the linear motor 82, whereby drawing of the low-pressure cooling medium gas into the compression chamber 76, compression of the cooling medium gas in the compression chamber 76, and discharge of the compressed high-pressure cooling medium gas from the compression chamber 76 are repeatedly carried out.
By the way, in the above-mentioned linear compressor 100, even when a current or voltage applied to the linear motor 82 is kept at a constant value, if the state of the load applied onto the linear compressor changes, the stroke of the piston 72 changes. Therefore, especially in a refrigeration compressor using the linear compressor 100, since the thermodynamic efficiency of a refrigerating cycle is significantly improved by controlling the flow of the cooling medium according to the varying environmental temperature, a means for detecting the stroke of the piston 72 that determines the flow of cooling medium (piston stroke detection means) is needed.
Further, in the linear compressor 100, from its structural viewpoint, there is a danger in that the front end of the piston might collide with the upper wall of the cylinder.
To be specific, the piston 72 receives not only the piston driving force of the linear motor 82 and the elasticity of the support spring 81 but also a force caused by a differential pressure between the pressure of the cooling medium gas in the compression chamber 76 and the back pressure of the piston 72, whereby the center position of the reciprocating motion of the piston 72 (hereinafter also referred to as piston amplitude center position) is offset with respect to the piston amplitude center position when the differential pressure is zero, i.e., the piston position when the support spring is not deformed (piston neutral position). Therefore, when the internal pressure of the compression chamber 76 that acts on the piston 72 is increased/decreased due to a change of the load state, not only the stroke of the piston 72 but also the center position of the reciprocating motion of the piston 72 might change.
In order to prevent collision of the piston with the cylinder, not only the stroke detection means but also a position detection means for detecting the distance between the front end of the piston and the inner wall of the cylinder head are required. For example, in a linear compressor having no collision prevention means, the front end of the piston hits the inner wall of the cylinder head, resulting in uncomfortable noise or damage to the piston or the cylinder.
There is employed, as the above-mentioned position detection means, a sensor which can detect the degree of displacement of the piston (piston displacement) with respect to the piston reference position such as the piston neutral position, without contacting the movable members such as the piston in the linear compressor 100. For example, a displacement meter using an eddy current system, a displacement meter using a differential transformer, and the like are employed.
However, when such sensor is used, the production cost of the linear compressor 100 is increased and, moreover, a space for mounting the sensor is needed, which leads to an increase in the size of the cabinet 71 of the linear compressor 100. Further, since the sensor is used while being exposed to a high-temperature and high-pressure gas in the compressor 100, there occurs a problem with then reliability of the sensor itself, in other words, a problem in that a sensor which can be reliably used under a high-temperature and high-pressure atmosphere is desired.
So, as a method for detecting the position of the piston 72, there is proposed a method of directly measuring the linear motor driving current and voltage which are supplied to the linear compressor 100, and deriving the position of the piston 72 on the basis of the measured values without using a position sensor placed in the linear compressor 100 (refer to Japanese Unexamined Patent Publication No. Hei. 8-508558).
Hereinafter, a description will be given of a piston position detection method used for a linear compressor, which is described in the above-mentioned literature.
FIG. 8 is a diagram illustrating an equivalent circuit of a linear motor for driving a piston of a linear compressor.
In FIG. 8, L indicates an equivalent inductance [H] of a coil as a component of the linear motor, and R indicates an equivalent resistance [xcexa9] of the coil. Further, V indicates an instantaneous voltage [V] applied to the linear motor, and I indicates a current [A] applied to the linear compressor. Further, xcex1xc3x97v indicates an induced electromotive voltage [V] which is generated when the linear motor is driven, wherein xcex1 is a thrust constant [N/A] of the linear motor, and v is an instantaneous velocity [m/s] of the linear motor.
The thrust constant xcex1 of the linear motor indicates a force [N] which is generated when a unit current [A] is passed through the linear motor. Although the unit of the thrust constant xcex1 is expressed by [N/A], this unit is equivalent to [Wb/m] or [Vxc2x7s/m].
The equivalent circuit shown in FIG. 8 is derived from the Kirchhoff""s law, and an instantaneous velocity v [m/s] of the linear motor is obtained from the equivalent circuit.
That is, under the driving state of the linear motor, the voltage (V) applied to the linear motor is balanced with the sum of a dropped voltage (Ixc3x97R) [V] due to the equivalent resistance of the coil of the linear motor, a dropped voltage (Lxc2x7dI/dt) [V] due to the equivalent inductance of the coil, and the induced electromotive voltage (xcex1xc3x97v) [V] that is generated when driving the linear motor, and the following formula (1) holds.                     v        =                              1            α                    ⁢                      (                          V              -                              R                xc3x97                I                            -                              L                ⁢                                                      ⅆ                    I                                                        ⅆ                    t                                                                        )                                              (        1        )            
The coefficients xcex1[N/A], R[xcexa9], and L[H] used in formula (1) are constants unique to the motor, and these constants are already-known values. Accordingly, the instantaneous velocity v[m/s] can be obtained from these constants and the applied voltage V[V] and current I[A], which are measured, on the basis of formula (1).
Further, a piston displacement (a distance from an undefined reference position to the piston) xc3x97[m] is obtained by a time integration of the instantaneous velocity v[m/s] as represented by the following formula (2). In formula (2), the constant Const. is the piston displacement at the start of integration.
xe2x80x83x=∫vdt+Const.xe2x80x83xe2x80x83(2)
As described above, in the piston position detection method disclosed in the above-described literature, the measured values V and I of the applied voltage and current to the linear motor are subjected to arithmetic processing including differentiation based on formula (1) to obtain the instantaneous velocity v of the piston, and further, the instantaneous velocity v is subjected to arithmetic processing including integration based on formula (2), whereby the piston displacement x can be calculated.
However, the piston displacement x obtained by the arithmetic processing based on formulae (1) and (2) is a displacement with reference to a certain position on the piston axis, and a distance from the cylinder head to the piston top dead point position cannot be obtained directly from the displacement x.
To be specific, when the linear compressor 100 is under a loaded condition, the piston center position (piston amplitude center position) in the piston reciprocating motion is offset with respect to the piston neutral position (i.e., the piston amplitude center position when the pressure in the compression chamber is equal to the back pressure) by the pressure of the cooling medium gas, and the piston reciprocates around the offset piston amplitude center position. In other words, the piston displacement x obtained by formula (2) includes an average component.
However, every actual analog integrator or digital integrator does not perform ideal integration processing for outputting a perfect response signal with respect to a constant or a DC input, but it is restricted in responding to a DC input. Therefore, an actual integrator cannot subject the piston displacement x to integration processing in which its average component is reflected. The reason why the DC response of the actual integrator is restricted is because the output of the integrator should be prevented from being saturated by an unavoidable DC component in the input signal.
As a result, the piston displacement x[m] obtained by the integration processing based on formula (2) using an actual integrator is not a displacement from which an actual distance between the piston and the cylinder head can be directly obtained, but a displacement simply indicating the piston position with reference to a certain point on the piston axis.
Therefore, the piston displacement x[m] obtained from formula (2) is converted into a piston displacement xxe2x80x2 indicating the piston position with respect to the piston amplitude center position. Further, using the converted piston displacement xxe2x80x2, arithmetic processing for obtaining a piston displacement xxe2x80x3 with reference to the cylinder head and indicating the piston amplitude center position is carried out.
Hereinafter, these arithmetic processings will be described in detail.
FIG. 9 is a diagram schematically illustrating the piston position in the cylinder.
Initially, the three coordinate systems shown in FIG. 9, i.e., a first coordinate system X, a second coordinate system Xxe2x80x2, and a third coordinate system Xxe2x80x3, will be briefly described.
The first coordinate system X is a coordinate system expressing the piston displacement x, and the first coordinate system X has, as an origin (x=0), a certain point Paru on the piston axis. Accordingly, the absolute value of the displacement x indicates the distance from the point Paru to the piston front end position P.
The second coordinate system Xxe2x80x2 is a coordinate system expressing the piston displacement xxe2x80x2, and the second coordinate system Xxe2x80x2 has, as an origin (xxe2x80x2=0), the piston amplitude center position Pav. Accordingly, the absolute value of the displacement xxe2x80x2 indicates the distance from the amplitude center position Pav to the piston front end position P.
The third coordinate system Xxe2x80x3 is a coordinate system expressing the piston displacement xxe2x80x3, and the third coordinate system Xxe2x80x3 has, as an origin (xxe2x80x3=0), the cylinder head position Psh on the piston axis. Accordingly, the absolute value of the displacement xxe2x80x3 indicates the distance from the cylinder head position Psh to the piston front end position P.
Next, an arithmetic operation for obtaining the piston displacement xxe2x80x3 will be described.
A piston position (piston top dead point position) Ptd in which the piston is closest to the cylinder head 75 is indicated by a displacement xtd on the first coordinate system X, and a piston position (piston bottom dead point position) Pbd in which the piston is farthest from the cylinder head 75 is indicated by a displacement xbd on the first coordinate system X. Then, a piston stroke Lps[m] is obtained from a difference between the displacement xtd corresponding to the piston top dead point position Ptd on the first coordinate system X and the displacement xbd corresponding to the piston bottom dead point position Pbd on the first coordinate system X.
Further, the piston amplitude center position Pav in the state where the piston is reciprocating is a position which is apart from the displacement xtd of the piston position (piston top dead point position) Ptd in which the piston is closest to the cylinder head by a length (Lps/2) that is equal to half the piston stroke Lps[m] from the cylinder head. Accordingly, the piston amplitude center position Pav is expressed by a displacement xav (=(xbdxe2x88x92xtd)/2) on the first coordinate system X.
Further, when the constant Const. in formula (2) is zero, a new function that indicates the piston position P by the piston displacement xxe2x80x2[m] is derived with the piston amplitude center position Pav as a reference (origin), in other words, on the second coordinate system Xxe2x80x2.
Next, a description will be given of a method for obtaining the piston displacement xxe2x80x3 indicating the piston amplitude center position on the third coordinate system Xxe2x80x3 with the cylinder head position Psh as an origin.
Under the state where the linear compressor 100 draws in the cooling medium gas (inlet state), i.e., under the state where the inlet valve is open, both the pressure in the compression chamber and the pressure on the back of the piston are equal to the cooling medium gas inlet pressure. This is because the linear compressor 100 is constructed so that the differential pressure becomes 0 under the state where the inlet valve is open. In this state, a force from the pressure of the cooling medium gas onto the piston can be ignored. That is, in this state, the forces acting on the piston are only the repulsive force of the spring that is generated by the bending (deformation) of the support spring 81, and the electromagnetic force that is generated by applying a current to the linear motor. According to the Newton""s law of motion, the sum of these forces is equal to the product of the total mass of the movable member that is moving and its acceleration.
Accordingly, under this state, the following formula (3) holds as an equation of motion relating to the movable member.
m=a=xcex1xc3x97Ixe2x88x92k(xxe2x80x2+xavxe2x80x3xe2x88x92xinixe2x80x3)xe2x80x83xe2x80x83(3)
In formula (3), m is the total mass [kg] of the movable member that is reciprocating, a is the instantaneous acceleration [m/s2] of the movable member, and k is the spring constant [N/m] of the support spring that is incorporated in the linear compressor. Further, xavxe2x80x3 is the above-mentioned displacement on the third coordinate system Xxe2x80x3, which indicates the piston amplitude center position, and the absolute value of this displacement xavxe2x80x3 expresses the distance from the cylinder head position Psh to the piston amplitude center position pav. Further, xinixe2x80x3 is the displacement on the third coordinate system Xxe2x80x3, which indicates the piston neutral position Pini, and the absolute value of this displacement xinixe2x80x3 expresses the distance [m] between the piston neutral position (the position of the piston in the state where the support spring is not deformed) Pini and the cylinder head position Psh.
The instantaneous acceleration a[m/s2] is obtained as shown in the following formula (4) by differentiating the instantaneous velocity v[m/s] expressed by formula (1).                     a        =                              ⅆ            v                                ⅆ            t                                              (        4        )            
Furthermore, the displacement xxe2x80x2[m] on the second coordinate system Xxe2x80x2, which indicates the distance from the piston amplitude center position Pav to the piston front end position P, is obtained by setting the constant Const. in formula (2) at 0.
Furthermore, the total mass m[kg] of the movable member, the spring constant k[N/m] of the support spring, and the displacement xinixe2x80x3 on the third coordinate system Xxe2x80x3, which indicates the distance from the cylinder head position Psh to the piston neutral position Pini, are already known values, and the driving current I may be the measured value.
Accordingly, the displacement xavxe2x80x3 on the third coordinate system Xxe2x80x3, which indicates the distance from the cylinder head position Psh to the piston amplitude center position Pav, can be calculated using formula (3).
Further, the displacement xtdxe2x80x3[m] on the third coordinate system Xxe2x80x3, which indicates the top dead point position of the piston (the position where the piston is closest to the cylinder head), can be obtained as a displacement in a position which is apart from the displacement xavxe2x80x3 on the third coordinate system Xxe2x80x3 obtained by formula (3) (the distance from the cylinder head position Psh to the piston amplitude center position Pav) by a distance that is equal to half of (Lps/2) the already-obtained piston stroke length Lps[m] toward the cylinder head.
In this way, the piston stroke length Lps[m] and the displacement xtdxe2x80x3[m] on the third coordinate system Xxe2x80x3, which indicates the piston top dead point position Ptd as a distance from the cylinder head position Psh, are calculated from the current I and voltage V which are applied to the linear compressor.
However, in the piston position detection method of the conventional linear compressor 100, since the piston displacement xxe2x80x2, which relatively indicates the piston position P with reference to the piston amplitude center position Pav, is calculated using the integrator and the differentiator, it is not possible to detect the piston position with high accuracy. That is, when the actual integrator and differentiator are constituted by analog circuits, ideal operations cannot be expected because of variations in parts, variations in characteristics due to temperature, and the like. On the other hand, when the integrator and differentiator are constituted by digital circuits, ideal operations cannot be expected because of the absence of data in sampling and holding.
Furthermore, when the piston position detecting circuit in the linear compressor is constituted by digital circuits, it is conceivable that the measuring cycle of the current I and the voltage V applied to the linear compressor may be reduced to increase the position detection accuracy. However, when the measuring cycle is reduced, the calculation cycle is also reduced, whereby the arithmetic load in the digital circuit is increased. Accordingly, when the measuring cycle is reduced, the performance of the microcomputer constituting the digital arithmetic circuit must be enhanced.
The present invention is made to solve the above-described problems and its object is to provide a linear compressor driving apparatus which can detect the position of a piston with high accuracy, on the basis of measured values of a driving current and a driving voltage applied to a linear compressor, without increasing loads of arithmetic processing using these measured values.
A linear compressor driving apparatus according to a first aspect of the present invention is a linear compressor driving apparatus for driving a linear compressor which has a piston and a linear motor for making the piston reciprocate and which generates a compressed gas by the reciprocating motion of the piston with an AC voltage being applied to the linear motor. The linear compressor apparatus according to the first aspect of the present invention comprises: an inverter for outputting an AC voltage and an AC current to the linear motor; a resonance frequency information output means for outputting resonance frequency information which indicates a resonance frequency of the reciprocating motion of the piston; a voltage detection means for detecting an output voltage of the inverter to output a voltage detection signal; a current detection means for detecting an output current of the inverter to output a current detection signal; an inverter controller for controlling the inverter on the basis of the resonance frequency information so that the inverter outputs, as an output voltage and output current, a sinusoidal-wave-shaped voltage and a sinusoidal-wave-shaped current whose frequencies match the resonance frequency of the piston reciprocating motion, respectively; a timing detection means for detecting, as a specific phase timing, a phase timing at which a differentiated value of the output current of the inverter becomes zero; and a piston velocity calculation means for receiving the voltage detection signal and the current detection signal, and calculating a maximum amplitude of a piston velocity in the piston reciprocating motion on the basis of instantaneous values of the output voltage and the output current from the inverter at the specific phase timing.
According to a second aspect of the present invention, in accordance with the linear compressor driving apparatus of the first aspect, the timing detection means detects, as the specific phase timing, a phase timing at which the amplitude of the output current from the inverter becomes maximum.
According to a third aspect of the present invention, in accordance with the linear compressor driving apparatus of the first aspect, the timing detection means detects a phase timing at which the phase of the output AC current from the inverter becomes at least one of 90xc2x0 and 270xc2x0, as the specific phase timing, on the basis of the current detection signal.
According to a fourth aspect of the present invention, in accordance with the linear compressor driving apparatus of the third aspect, the inverter is provided with an inverter controller for outputting an inverter driving control signal which drives and controls the inverter; and the timing detection means detects a phase timing at which a differentiated value of the output current from the inverter becomes zero on the basis of the phase of the inverter driving control signal.
According to a fifth aspect of the present invention, in accordance with the linear compressor driving apparatus of the fourth aspect, the timing detection means has a phase shift amount detector for detecting the amount of phase shift of the phase of the inverter driving control signal from the phase of the output current of the inverter, and detects a phase timing at which a differentiated value of the output current of the inverter becomes zero, on the basis of the inverter driving control signal whose phase is corrected so that the amount of phase shift becomes zero.
According to a sixth aspect of the present invention, in the linear compressor driving apparatus of the first apparatus, the piston velocity calculation means performs a temperature correction process on a thrust constant of the linear motor, whose value varies with variations in temperature, and calculates a maximum amplitude of the piston velocity on the basis of the temperature-corrected thrust constant, the instantaneous current value, the instantaneous voltage value, and an internal resistance value of the linear motor.
According to a seventh aspect of the present invention, in accordance with the linear compressor driving apparatus of the first aspect, the piston velocity calculation means performs a temperature correction process on an internal resistance value of the linear motor, whose value varies with variations in temperature, and calculates a maximum amplitude of the piston velocity on the basis of the temperature-corrected internal resistance value, the instantaneous values of the output voltage and output current of the inverter, and a thrust constant of the linear motor.
According to an eighth aspect of the present invention, in accordance with the linear compressor driving apparatus of the first aspect, the piston velocity calculation means repeats a velocity calculation process for calculating a maximum amplitude of the piston velocity, and in each of the repeated velocity calculation processes, the piston velocity calculation means corrects a thrust constant of the linear motor, whose value varies with variations in the piston velocity, on the basis of a maximum amplitude of the piston velocity which is calculated in a previous velocity calculation process, and calculates a maximum amplitude of the piston velocity on the basis of the corrected thrust constant.
According to a ninth aspect of the present invention, the linear compressor driving apparatus of the first aspect further includes a stroke information calculation means for calculating piston stroke information which indicates a maximum amplitude of a piston displacement in the piston reciprocating motion on the basis of the output voltage of the inverter and the frequency of the output current of the inverter, which are determined by the inverter controller, and the maximum amplitude of the piston velocity that is calculated by the piston velocity calculation means.
According to a tenth aspect of the present invention, the linear compressor driving apparatus of the first aspect further includes a bottom dead point position information calculation means for calculating bottom dead point position information which indicates a piston bottom dead point position in the piston reciprocating motion on the basis of the output voltage of the inverter and the frequency of the output current of the inverter, which are determined by the inverter controller, and the maximum amplitude of the piston velocity that is calculated by the piston velocity calculation means.
According to an eleventh aspect of the present invention, the linear compressor driving apparatus of the ninth aspect further includes: a bottom dead point position information calculation means for calculating bottom dead point position information which indicates a piston bottom dead point position in the piston reciprocating motion on the basis of the output voltage of the inverter and the frequency of the output current of the inverter, which are determined by the inverter controller, and the maximum amplitude of the piston velocity that is calculated by the piston velocity calculation means; and an arithmetic means for calculating center position information which indicates a piston center position in the piston reciprocating motion by performing the four fundamental rules of arithmetic on the basis of the bottom dead point position information and the piston stroke information.
According to a twelfth aspect of the present invention, the linear compressor driving apparatus of the ninth aspect further includes: a bottom dead point position information calculation means for calculating bottom dead point position information which indicates a piston bottom dead point position in the piston reciprocating motion, on the basis of the output voltage of the inverter and the frequency of the output current of the inverter, which are determined by the inverter controller, and the maximum amplitude of the piston velocity which is calculated by the piston velocity calculation means; and an arithmetic means for calculating top dead point position information indicating a piston top dead point position in the piston reciprocating motion by performing the four fundamental rules of arithmetic on the basis of the bottom dead point position information and the piston stroke information.
According to a thirteenth aspect of the present invention, the linear compressor driving apparatus of the ninth aspect further includes: a top dead point position information detection sensor for detecting a piston top dead point position in the piston reciprocating motion to output top dead point position information indicating the detected position; and an arithmetic means for calculating center position information indicating a piston center position in the piston reciprocating motion by performing the four fundamental rules of arithmetic on the basis of the top dead point position information and the piston stroke information.
According to a fourteenth aspect of the present invention, the linear compressor driving apparatus of the ninth aspect further includes: a top dead point position information detection sensor for detecting a piston top dead point position in the piston reciprocating motion to output top dead point position information indicating the detected position; and an arithmetic means for calculating bottom dead point position information indicating a piston bottom dead point position in the piston reciprocating motion by performing the four fundamental rules of arithmetic on the basis of the top dead point position information and the piston stroke information.
According to a fifteenth aspect of the present invention, the linear compressor driving apparatus of the ninth aspect further includes: a bottom dead point position information detection sensor for detecting a piston bottom dead point position in the piston reciprocating motion; and an arithmetic means for calculating center position information indicating a piston center position in the piston reciprocating motion by performing the four fundamental rules of arithmetic on the basis of the bottom dead point position information and the piston stroke information.
According to a sixteenth aspect of the present invention, the linear compressor driving apparatus of the ninth aspect further includes: a bottom dead point position information detection sensor for detecting a piston bottom dead point position in the piston reciprocating motion to output bottom dead point position information indicating the detected position; and an arithmetic means for calculating top dead point position information indicating a piston top dead point position in the piston reciprocating motion by performing the four fundamental rules of arithmetic on the basis of the bottom dead point position information and the piston stroke information.
According to a seventeenth aspect of the present invention, the linear compressor driving apparatus of the ninth aspect further includes: a center position information calculation means for calculating center position information indicating a piston center position in the piston reciprocating motion on the basis of the output current from the inverter; and an arithmetic means for calculating top dead point position information indicating a piston top dead point position in the piston reciprocating motion by performing the four fundamental rules of arithmetic on the basis of the center position information and the piston stroke information.
According to an eighteenth aspect of the present invention, the linear compressor driving apparatus of the ninth aspect further includes: a center position information calculation means for calculating center position information indicating a piston center position in the piston reciprocating motion on the basis of the output current from the inverter; and an arithmetic means for calculating bottom deal point position information indicating a piston bottom dead point position in the piston reciprocating motion by performing the four fundamental rules of arithmetic on the basis of the center position information and the piston stroke information.
According to a nineteenth aspect of the present invention, in accordance with the linear compressor driving apparatus of either the tenth through twelfth aspects, the linear compressor has an elastic member which applies a force to the piston so as to bring the piston back to its neutral position when the piston is displaced from the neutral position; and the bottom dead point position information calculation means calculates, as the bottom dead point position information, position information indicating the piston bottom dead point position relative to the piston neutral position on the basis of the output voltage of the inverter and the frequency of the output current of the inverter, which are determined by the inverter controller, the maximum amplitude of the piston velocity which is calculated by the piston velocity calculation means, the weight of the movable member which performs the piston reciprocating motion in the linear compressor, and the spring constant of the elastic member.
According to a twentieth aspect of the present invention, in the linear compressor driving apparatus of the ninth aspect, the piston stroke calculation means repeats a calculation process for calculating the piston stroke information on the basis of the maximum amplitude of the piston velocity, where in each of the repeated calculation processes, the piston stroke calculation means corrects a thrust constant of the linear motor, whose value varies with variations in the piston position, on the basis of the piston stroke information calculated in a previous calculation process, and calculates the piston stroke information on the basis of the corrected thrust constant.
A linear compressor driving apparatus according to a twenty-first aspect of the present invention is a linear compressor driving apparatus for driving a linear compressor which has a piston and a linear motor for reciprocating the piston and which generates a compressed gas by the reciprocating motion of the piston with an AC voltage being applied to the linear motor. The linear compressor driving apparatus according to the twenty-first aspect comprises: an inverter for outputting an AC voltage and an AC current to the linear motor; a resonance frequency information output means for outputting resonance frequency information that indicates a resonance frequency of the piston reciprocating motion; a current detection means for detecting an output current of the inverter to output a current detection signal; an inverter controller for controller the inverter on the basis of the resonance frequency information so that the inverter outputs, as an output voltage and output current, a sinusoidal-wave-shaped voltage and a sinusoidal-wave-shaped current whose frequencies match the resonance frequency of the piston reciprocating motion, respectively; a timing detection means for detecting, as a specific phase timing, a phase timing at which a differentiated value of the output current of the inverter becomes zero; and a piston center position calculation means for calculating position information indicating a piston center position in the piston reciprocating motion on the basis of an instantaneous value of the output current of the inverter at the specific phase timing, with reference to a piston position where a pressure difference between the pressure of a cooling medium gas that is discharged from the linear compressor and the pressure of the cooling medium gas that is drawn into the linear compressor becomes zero.
According to a twenty-second aspect of the present invention, in the linear compressor driving apparatus of the twenty-first aspect, the linear compressor has an elastic member which applies a force to the piston so as to bring the piston back to its neutral position when the piston is displaced from the neutral position; and the center position information calculation means calculates, as the center position information, position information indicating the piston center position relative to the piston neutral position on the basis of the maximum amplitude of the output current from the inverter, the thrust constant of the linear motor, and the spring constant of the elastic member.
According to a twenty-third aspect of the present invention, the linear compressor driving apparatus of the twenty-first aspect further includes: a discharge pressure detection means for detecting the pressure of the cooling medium gas that is discharged from the linear compressor; and an inlet pressure detection means for detecting the pressure of the cooling medium gas that is drawn into the linear compressor; wherein the center position information calculation means calculates an action force in the direction of the piston reciprocating motion, which force acts on the piston from the cooling medium gas, on the basis of the pressure difference between the discharge pressure and the inlet pressure, and then calculates, as the center position information, position information indicating the piston center position relative to the piston position where the pressure difference becomes zero, on the basis of the calculated action force.
According to a twenty-fourth aspect of the present invention, in accordance with the linear compressor driving apparatus of the twenty-third aspect, the center position information calculation means calculates an action force in the direction of the piston reciprocating motion, which force acts on the piston from the cooling medium gas, on the basis of the pressure difference between the discharge pressure and the inlet pressure and the resonance frequency indicated by the resonance frequency information, and then calculates, as the center position information, position information indicating the piston center position relative to the piston position where the pressure difference becomes zero on the basis of the calculated action force.
As described above, according to the first aspect of the present invention, there is provided a linear compressor driving apparatus for driving a linear compressor which has a piston and a linear motor for making the piston reciprocate, and generates a compressed gas by the reciprocating motion of the piston, with an AC voltage being applied to the linear motor, and this apparatus comprises: an inverter for outputting an AC voltage and an AC current to the linear motor; a resonance frequency information output means for outputting resonance frequency information which indicates a resonance frequency of the reciprocating motion of the piston; a voltage detection means for detecting an output voltage of the inverter to output a voltage detection signal; a current detection means for detecting an output current of the inverter to output a current detection signal; an inverter controller for controlling the inverter on the basis of the resonance frequency information so that the inverter outputs, as the output voltage and output current of the inverter, a sinusoidal-wave-shaped voltage and a sinusoidal-wave-shaped current whose frequencies match the resonance frequency of the piston reciprocating motion, respectively; a timing detection means for detecting, as a specific phase timing, a phase timing at which a differentiated value of the output current of the inverter becomes zero; and a piston velocity calculation means for receiving the voltage detection signal and the current detection signal, and calculating a maximum amplitude of a piston velocity in the piston reciprocating motion on the basis of instantaneous values of the output voltage and the output current from the inverter at the specific phase timing. Therefore, a displacement of the piston can be easily and accurately obtained on the basis of the driving current and driving voltage of the linear compressor without having to use complicated calculations such as integration and differentiation.
According to the second aspect of the present invention, in accordance with the linear compressor driving apparatus of the first aspect, the timing detection means detects, as the specific phase timing, a phase timing at which the amplitude of the output current from the inverter becomes maximum. Therefore, in an arithmetic formula for calculating the piston velocity from the driving current and driving voltage of the linear compressor, a term including the differentiated value of the driving-current can be deleted as being zero.
According to the third aspect of present invention, in accordance with the linear compressor driving apparatus of the first aspect, the timing detection means detects a phase timing at which the phase of the output AC current from the inverter becomes at least one of 90xc2x0 and 270xc2x0, as the specific phase timing, on the basis of the current detection signal. Therefore, in an arithmetic formula for calculating the piston velocity from the driving current and the driving voltage of the linear compressor, a term including the differentiated value of the driving current can be deleted as being zero.
According to the fourth aspect of the present invention, in accordance with the linear compressor driving apparatus of the third aspect, the inverter is provided with an inverter controller for outputting an inverter driving control signal which drives and controls the inverter; and the timing detection means detects a phase timing at which a differentiated value of the output current from the inverter becomes zero on the basis of the phase of the inverter driving control signal. Therefore, in an arithmetic formula for calculating the piston velocity from the driving current and driving voltage of the linear compressor, a term including the differentiated value of the driving current can be deleted.
According to the fifth aspect of the present invention, in accordance with the linear compressor driving apparatus of the fourth aspect, the timing detection means has a phase shift amount detector for detecting the amount of phase shift of the phase of the inverter driving control signal from the phase of the output current of the inverter, and detects a phase timing at which a differentiated value of the output current of the inverter becomes zero, on the basis of the inverter driving control signal whose phase is corrected so that the amount of phase shift becomes zero. Therefore, a phase timing at which the differentiated value of the output current of the inverter becomes zero can be correctly detected on the basis of the inverter driving control signal.
According to the sixth aspect of the present invention, in accordance with the linear compressor driving apparatus of the first aspect, the piston velocity calculation means performs a temperature correction process on a thrust constant of the linear motor, whose value varies with variations in temperature, and calculates a maximum amplitude of the piston velocity on the basis of the temperature-corrected thrust constant, the instantaneous current value, the instantaneous voltage value, and an internal resistance value of the linear motor. Therefore, the maximum amplitude of the piston velocity can always be detected with accuracy, irregardless of variations in the thrust constant of the linear motor due to variations in the temperature of the linear compressor.
According to the seventh aspect of the present invention, in accordance with the linear compressor driving apparatus of the first aspect, the piston velocity calculation means performs a temperature correction process on an internal resistance value of the linear motor, whose value varies with variations in temperature, and calculates a maximum amplitude of the piston velocity on the basis of the temperature-corrected internal resistance value, the instantaneous values of the output voltage and output current of the inverter, and a thrust constant of the linear motor. Therefore, the maximum amplitude of the piston velocity can always be detected with accuracy, irregardless of variations in the internal resistance value of the linear motor due to variations in the temperature of the linear compressor.
According to the eighth aspect of the present invention, in accordance with the linear compressor driving apparatus of the first aspect, the piston velocity calculation means repeats a velocity calculation process for calculating a maximum amplitude of the piston velocity, and in each of the repeated velocity calculation processes, the piston velocity calculation means corrects a thrust constant of the linear motor, whose value varies with variations in the piston velocity, on the basis of a maximum amplitude of the piston velocity which is calculated in the previous velocity calculation process, and calculates a maximum amplitude of the piston velocity on the basis of the corrected thrust constant. Therefore, the maximum amplitude of the piston velocity can always be detected with accuracy, irregardless of variations in the thrust constant of the linear motor due to variations in the piston velocity.
According to the ninth aspect of the present invention, the linear compressor driving apparatus of the first aspect further includes a stroke information calculation means for calculating piston stroke information which indicates a maximum amplitude of a piston displacement in the piston reciprocating motion on the basis of the output voltage of the inverter and the frequency of the output current of the inverter, which are determined by the inverter controller, and the maximum amplitude of the piston velocity that is calculated by the piston velocity calculation means. Therefore, the driving ability of the linear compressor can be controlled on the basis of the piston stroke information.
According to the tenth aspect of the present invention, the linear compressor driving apparatus of the first aspect further includes a bottom dead point position information calculation means for calculating bottom dead point position information which indicates a piston bottom dead point position in the piston reciprocating motion on the basis of the output voltage of the inverter and the frequency of the output current of the inverter, which are determined by the inverter controller, and the maximum amplitude of the piston velocity that is calculated by the piston velocity calculation means. Therefore, the amount of flexure of the resonance spring can be grasped according to the piston bottom dead point position information. Thereby, driving control of the linear compressor can also be carried out on the basis of the amount of flexure of the resonance spring so that the resonance spring is not deformed beyond its destruction limits.
According to the eleventh aspect of the present invention, the linear compressor driving apparatus in the ninth aspect further includes: a bottom dead point position information calculation means for calculating bottom dead point position information which indicates a piston bottom dead point position in the piston reciprocating motion on the basis of the output voltage of the inverter and the frequency of the output current of the inverter, which are determined by the inverter controller, and the maximum amplitude of the piston velocity that is calculated by the piston velocity calculation means; and an arithmetic means for calculating center position information which indicates a piston center position in the piston reciprocating motion by performing the four fundamental rules of arithmetic on the basis of the bottom dead point position information and the piston stroke information. Therefore, the linear compressor can be controlled on the basis of the piston center position information so that the piston vibration center position matches the position where the maximum efficiency of the linear motor can be achieved, whereby the linear compressor driving efficiency can be further enhanced.
According to the twelfth aspect of the present invention, the linear compressor driving apparatus of the ninth aspect further includes: a bottom dead point position information calculation means for calculating bottom dead point position information which indicates a piston bottom dead point position in the piston reciprocating motion on the basis of the output voltage of the inverter and the frequency of the output current of the inverter, which are determined by the inverter controller, and the maximum amplitude of the piston velocity which is calculated by the piston velocity calculation means; and an arithmetic means for calculating top dead point position information indicating a piston top dead point position in the piston reciprocating motion by performing the four fundamental rules of arithmetic on the basis of the bottom dead point position information and the piston stroke information. Therefore, the possibility of collision between the piston and the cylinder head can be judged with high accuracy on the basis of the top dead point position information.
According to the thirteenth aspect of the present invention, the linear compressor driving apparatus of the ninth aspect further includes: a top dead point position information detection sensor for detecting a piston top dead point position in the piston reciprocating motion to output top dead point position information indicating the detected position; and an arithmetic means for calculating center position information indicating a piston center position in the piston reciprocating motion by performing the four fundamental rules of arithmetic on the basis of the top dead point position information and the piston stroke information. Therefore, the linear compressor can be controlled by using a simple sensor so that the piston vibration center position matches the position where the maximum efficiency of the linear motor can be achieved, whereby the linear compressor driving efficiency can be further enhanced.
According to the fourteenth aspect of the present invention, the linear compressor driving apparatus of the ninth aspect further includes: a top dead point position information detection sensor for detecting a piston top dead point position in the piston reciprocating motion to output top dead point position information indicating the detected position; and an arithmetic means for calculating bottom dead point position information indicating a piston bottom dead point position in the piston reciprocating motion by performing the four fundamental rules of arithmetic on the basis of the top dead point position information and the piston stroke information. Therefore, the linear compressor can be controlled by using a simple sensor so that the resonance spring is not deformed beyond the destruction limits on the basis of the piston bottom dead point position information.
According to the fifteenth aspect of the present invention, the linear compressor driving apparatus of the ninth aspect further includes: a bottom dead point position information detection sensor for detecting a piston bottom dead point position in the piston reciprocating motion; and an arithmetic means for calculating center position information indicating a piston center position in the piston reciprocating motion by performing the four fundamental rules of arithmetic on the basis of the bottom dead point position information and the piston stroke information. Therefore, the linear compressor can be controlled by using a simple sensor so that the piston vibration center position matches the position where the maximum efficiency of the linear motor can be achieved, whereby the linear compressor driving efficiency can be further enhanced.
According to the sixteenth aspect of the present invention, the linear compressor driving apparatus of the ninth aspect further includes: a bottom dead point position information detection sensor for detecting a piston bottom dead point position in the piston reciprocating motion to output bottom dead point position information indicating the detected position; and an arithmetic means for calculating top dead point position information indicating a piston top dead point position in the piston reciprocating motion by performing the four fundamental rules of arithmetic on the basis of the bottom dead point position information and the piston stroke information. Therefore, by using a simple sensor the risk of collision between the piston and the cylinder head can be judged on the basis of the top dead point position information.
According to the seventeenth aspect of the present invention , the linear compressor driving apparatus of the ninth aspect further includes: a center position information calculation means for calculating center position information indicating a piston center position in the piston reciprocating motion on the basis of the output current from the inverter; and an arithmetic means for calculating top dead point position information indicating a piston top dead point position in the piston reciprocating motion, by performing the four fundamental rules of arithmetic on the basis of the center position information and the piston stroke information. Therefore, the possibility of collision between the piston and the cylinder head can be judged with high accuracy on the basis of the top dead point position information.
According to the eighteenth aspect of the present invention, the linear compressor driving apparatus of the ninth aspect further includes: a center position information calculation means for calculating center position information indicating a piston center position in the piston reciprocating motion on the basis of the output current from the inverter; and an arithmetic means for calculating bottom deal point position information indicating a piston bottom dead point position in the piston reciprocating motion by performing the four fundamental rules of arithmetic on the basis of the center position information and the piston stroke information. Therefore, driving control of the linear compressor can also be carried out so that the resonance spring is not compressed beyond the destruction limits, on the basis of the piston bottom dead point position information.
According to the nineteenth aspect of the present invention, in accordance with the linear compressor driving apparatus of any of the tenth through twelfth aspects, the linear compressor has an elastic member which applies a force to the piston so as to bring the piston back to its neutral position when the piston is displaced from the neutral position; and the bottom dead point position information calculation means calculates, as the bottom dead point position information, position information indicating the piston bottom dead point position relative to the piston neutral position on the basis of the output voltage of the inverter and the frequency of the output current of the inverter, which are determined by the inverter controller, the maximum amplitude of the piston velocity which is calculated by the piston velocity calculation means, the weight of the movable member which performs the piston reciprocating motion in the linear compressor, and the spring constant of the elastic member. Therefore, the amount of flexure of the resonance spring can be determined according to the piston bottom dead point position information. Thereby, driving control of the linear compressor so as to prevent the resonance spring from being deformed beyond the destruction limits can be easily carried out on the basis of the amount of flexure of the resonance spring.
According to the twentieth aspect of the present invention, in accordance with the linear compressor driving apparatus of the ninth aspect, the piston stroke calculation means repeats a calculation process for calculating the piston stroke information on the basis of the maximum amplitude of the piston velocity, where in each of the repeated calculation processes, the piston stroke calculation means corrects a thrust constant of the linear motor, whose value varies with variations in the piston position, on the basis of the piston stroke information calculated in the previous calculation process, and calculates the piston stroke information on the basis of the corrected thrust constant. Therefore, the maximum amplitude of the piston velocity can always be detected with accuracy, irregardless of variations in the thrust constant of the linear motor due to variations in the piston position.
According to the twenty-first aspect of the present invention, there is provided a linear compressor driving apparatus for driving a linear compressor which has a piston and a linear motor for reciprocating the piston, and generates a compressed gas by the reciprocating motion of the piston, with an AC voltage being applied to the linear motor, and this apparatus comprises: an inverter for outputting an AC voltage and an AC current to the linear motor; a resonance frequency information output means for outputting resonance frequency information that indicates a resonance frequency of the piston reciprocating motion; a current detection means for detecting an output current of the inverter to output a current detection signal; an inverter controller for controller the inverter on the basis of the resonance frequency information so that the inverter outputs, as its output voltage and output current, a sinusoidal-wave-shaped voltage and a sinusoidal-wave-shaped current whose frequencies match the resonance frequency of the piston reciprocating motion, respectively; a timing detection means for detecting, as a specific phase timing, a phase timing at which a differentiated value of the output current of the inverter becomes zero; and a piston center position calculation means for calculating position information indicating a piston center position in the piston reciprocating motion on the basis of an instantaneous value of the output current of the inverter at the specific phase timing, with reference to a piston position where a pressure difference between the pressure of a cooling medium gas that is discharged from the linear compressor and the pressure of the cooling medium gas that is drawn into the linear compressor becomes zero. Therefore, the linear compressor can be controlled on the basis of the piston center position information so that the piston vibration center position matches the position where the maximum efficiency of the linear motor can be achieved, whereby the linear compressor driving efficiency can be further enhanced.
According to the twenty-second aspect of the present invention, in accordance with the linear compressor driving apparatus of the twenty-first aspect, the linear compressor has an elastic member which applies a force to the piston so as to bring the piston back to its neutral position, when the piston is displaced from the neutral position; and the center position information calculation means calculates, as the center position information, position information indicating the piston center position relative to the piston neutral position, on the basis of the maximum amplitude of the output current from the inverter, the thrust constant of the linear motor, and the spring constant of the elastic member. Therefore, the linear compressor can be controlled on the basis of the piston center position information so that the piston vibration center position matches the position where the maximum efficiency of the linear motor can be achieved, whereby the linear compressor driving efficiency can be further enhanced.
According to the twenty-third aspect of the present invention, the linear compressor driving apparatus of the twenty-first aspect further includes: a discharge pressure detection means for detecting the pressure of the cooling medium gas that is discharged from the linear compressor; and an inlet pressure detection means for detecting the pressure of the cooling medium gas that is drawn into the linear compressor; wherein the center position information calculation means calculates an action force in the direction of the piston reciprocating motion, which force acts on the piston from the cooling medium gas, on the basis of the pressure difference between the discharge pressure and the inlet pressure, and then calculates, as the center position information, position information indicating the piston center position relative to the piston position where the pressure difference becomes zero, on the basis of the calculated action force. Therefore, the linear compressor can be controlled on the basis of the piston center position information so that the piston vibration center position matches the position where the maximum efficiency of the linear motor can be achieved, whereby the linear compressor driving efficiency can be further enhanced.
According to the twenty-fourth aspect of the present invention, in accordance with the linear compressor driving apparatus of the twenty-third aspect, the center position information calculation means calculates an action force in the direction of the piston reciprocating motion, which force acts on the piston from the cooling medium gas, on the basis of the pressure difference between the discharge pressure and the inlet pressure, and the resonance frequency indicated by the resonance frequency information, and then calculates, as the center position information, position information indicating the piston center position relative to the piston position where the pressure difference becomes zero on the basis of the calculated action force. Therefore, the linear compressor can be controlled on the basis of the piston center position information so that the piston vibration center position matches the position where the maximum efficiency of the linear motor can be achieved, whereby the linear compressor driving efficiency can be further enhanced.